1. Field of the Invention
The present invention relates to a rear projection image display device for changing an optical path of an image from a projection device with a reflection mirror, and projecting the image onto a screen from the rear side.
2. Description of the Background Art
Recent years, much larger screen and much higher definition is required in a large screen display system (multi-vision or video wall) as a large monitor for a monitoring and controlling system and other similar systems, the large screen display system being obtained by stacking rear projection image display devices for changing an optical path of an image from a projection device with a reflection mirror and projecting the image onto a screen from the rear side, vertically and horizontally.
When a CRT projector was used as a projection device, electrical correction was added to the inputted image. Currently, higher definition of an image is required, and the mainstream is that the inputted image is projected onto a screen as it is without any electrical correction, by the use of a liquid crystal device, a digital image device, and other similar devices.
On the other hand, optical system distortion due to projection lens and image distortion due to deflection of a reflection mirror are caused in the rear projection image display device for changing an optical path of an image from a projection device with the reflection mirror, and projecting the image onto a screen from the rear side. Therefore, it is difficult to depict the inputted image onto the screen truly and without any lack of the image. Particularly these days, display devices are rapidly increased in size, so that image distortion is much easier to be recognized.
Here, the optical system distortion due to the projection lens and the image distortion due to the deflection of the reflection mirror will be described. As the optical system distortion due to the projection lens, pin distortion in which periphery of an image bows inwardly seen from a screen side, and barrel distortion in which periphery of an image bows outwardly in a pot-bellied shape, are well known.
When the reflection mirror is deflected by its own weight, it is also well known that the image projected from the projection device is produced as pin distortion as described above when seen on a screen.
As a countermeasure to correct the aforementioned image distortion, an image distortion correcting mechanism of a projection image display device is provided, including a reflection mirror having a trapezoidal opening, a support unit disposed near four corners of the opening of the reflection mirror so as to cover the opening, for supporting the reflection mirror, and an adjustment unit disposed near the center of each of four sides of the opening of the reflection mirror, for pressing the reflection mirror (see Japanese Patent Application Laid-Open No. 2002-77777, for example).
Further, a projection display device is provided, including an adjustment mechanism changing a flatness of the reflection mirror on the periphery in accordance with a necessary part unit of the reflection mirror (see Japanese Patent Application Laid-Open No. 2001-109071, for example). Still further, an image distortion correcting mechanism of a rear projection image display device is provided, including an adjustment fitting attached so as to correspond to a support fitting for supporting an upper side of the reflection mirror to be sandwiched therebetween, an adjustment screw and a nut for joining the support fitting and the adjustment fitting in the upper side of the reflection mirror, a support fitting being disposed in each side of the reflection mirror and including a plurality of screw holes to which each of the adjustment screws is attached, for supporting each side of the reflection mirror to be sandwiched between the both sides from back and front with the adjustment screw, and a plurality of adjusting screws attached to the screw holes, whereby the support fitting of the upper side of the reflection mirror is adjusted in the vicinity by the adjustment screw and the nut, and the number and position of the adjusting screws attached to the plurality of the screw holes are changed so as to correct deflection of the reflection mirror (see Japanese Patent Gazette No. 3972915, for example).
However, the image distortion correcting mechanism disclosed in Japanese Patent Application Laid-Open No. 2002-77777 had a problem that when the size of the reflection mirror is large, distortion correction does not make a screen linear on the periphery, resulting in an unnatural image. This is because the shape of the reflection mirror is changed only locally, if the size of the reflection mirror becomes larger and the side to be corrected becomes longer, since the reflection mirror is an elastic body, causing wavelike behavior of the reflection mirror. Particularly, the size of the reflection mirror is increasing according to the increase in size of a screen, so that the aforementioned image distortion cannot be ignored when seen on the screen.
As disclosed in Japanese Patent Application Laid-Open No. 2001-109071 and Japanese Patent Gazette No. 3972915, many correction points are prepared in the respective sides of the reflection mirror, and the reflection mirror is not deformed as extremely wavelike as in Japanese Patent Application Laid-Open No. 2002-77777 by correcting several points of the respective sides. As a result, the image of the corrected side looks like substantially linear on the periphery when seen from the screen side. However, several points are needed to be adjusted for one screen in order to correct image distortion of each side of the screen. Therefore, tremendous points are needed to be adjusted for one device in the large screen display system (multi-vision or video wall) obtained by stacking image devices vertically and horizontally, causing a lot of trouble and time in installing an image device. Particularly, since adjustment time and accuracy varies according to the ability of an operator who installs and adjusts a device, it has been difficult to correct image distortion uniformly. Further, many structures have been needed to be prepared, resulting in cost-intensive.